Dataminers have found strings for "Island 7" and "Island 8" in the game's code for years.

While rare, using third-party services is against terms of service.

Private servers in Dragon Mania are essentially custom-made game environments that allow players to experience the game with exclusive features and modifications. These servers are not officially supported by the game developers but are created by enthusiasts or private server hosting companies. By connecting to a private server, players can enjoy a unique and personalized experience, free from the limitations of the public game.

It sounds like you're referring to found only on a private server for Dragon Mania Legends (or a similar dragon collecting/training game).

Official DML limits you to a strict island count. Private server exclusives often unlock a hidden 25th or 30th island that was scrapped during development. Data miners have found terrain files labeled "Cloud City" and "Molten Core." On a PS, you can actually build on these ghost islands.